None.
This invention relates generally to steam boilers, and particularly concerns both a method and apparatus that may be utilized advantageously to install original and replacement boiler tubes in the drums of steam boilers such as those steam boilers that are typically operated at very high steam pressures (e.g., to approximately 1,600 psi) and high temperatures (e.g., to approximately 1,250xc2x0 F.) as in major electrical power generating plants in the United States.
In the United States, and in connection with the construction and maintenance of steam boilers operated at very high steam pressures (e.g., to approximately 1,600 pounds per square inch) it is common practice to provide the ends of installed boiler tubes with flared end terminations that are formed by swaging and that function to secure tubes in place in the cooperating boiler drum wall bores during boiler operation. The boiler tubes have outside diameters that typically range from 1 inch to 6 inches, and wall thicknesses that typically range from as little as approximately 0.100 inch to as much as approximately 0.250 inch. The end segments of such tubes, after the tubes have been bent to their proper installed configuration, are slidably inserted into co-operating tube bores provided in the walls of the steam boiler drum components, and their end terminations are expanded or flared radially outward through use of a conventional rotary swaging machine. In the conventional practice no attempt is made to expand portions of the tube that lie within the limits of the drum wall thickness to thereby improve the initial fit or match of the boiler tube external diameter to the drum tube bore internal diameter, and thus enhance securing the boiler tube end segments to the boiler drum.
I have discovered a method of physically securing a boiler tube end segment to a co-operating boiler drum component that eliminates having to provide the end segment with a terminating end flare, and that simultaneously enhances the fit of the tube outside diameter to the drum wall boiler tube bore inside diameter.
Also, I have discovered a boiler tube expansion tool construction that is effective to develop in the installed boiler tube end segment both: (1) an installed tube shear resistance strength that is at least as great as that of a comparable installed boiler tube end segment having a flared end termination, and (2) an enhanced installed match between the tube exterior diameter and the interior diameter of the co-operating drum boiler tube bore.
Other objects and advantages of the present invention will become apparent during consideration of the drawings, descriptions, and claims which follow.
The method of the present invention involves the essential steps of: (1) providing at least one circumferential groove in the interior surface of a boiler tube bore in the steam boiler drum wall, (2) sliding the end segment of a properly sized boiler tube into the drum wall grooved boiler tube bore sufficiently that its end termination is positioned flush with the drum wall interior wall surface, (3) containing an incompressible fluid in the boiler tube end segment in a zone within the limits of the drum wall thickness, and (4) developing an extremely high pressure (e.g., 100,000 pounds per square inch) in the incompressible fluid contained in the tube end segment to thereby expand boiler tube end segment metal into contact with the drum wall boiler tube bore and its included internal circumferential groove(s). Afterwards the fluid pressure within the boiler tube end segment is reduced to an ambient pressure, and the tool is withdrawn from within the installed tube end segment. The process is repeated for each additional boiler end segment in the steam boiler installation.
The boiler tube hydraulic expansion tool of the present invention is basically an assembly comprised of an actuator section, a co-operating fluid pressure multiplier section, and a conventional source of pressurized primary incompressible fluid for operating the apparatus actuator section. The fluid pressure multiplier section has a nose extension that carries suitably spaced-apart and longitudinally-restrained elastomeric fluid seal and metal seal back-up combinations, and that, when properly inserted into the boiler tube end segment which is to be expanded, completes the creation of a secondary fluid containment chamber. The so-created secondary fluid containment chamber receives, through the fluid pressure multiplier section nose extension, a preferred secondary incompressible fluid at a pressure that is a multiple of the pressure of the pressurized primary incompressible fluid. The primary and secondary incompressible fluids that are preferred for use in the invention tool assembly are conventional petroleum-based hydraulic fluid and water, respectively; the extent of pressure multiplication that is provided in the invention boiler tube segment expansion tool is generally in the range of increasing a 2,000 psi primary fluid operating pressure to a 100,000 psi secondary incompressible fluid metal expansion pressure.